Hydraulic mine prop



Aug. 25, 1964 K. M, GRoE'rscHEL 3,145,964

HYDRAULIC MINE PROP Filed May 9, 1965 PRESSURE MEDIUM SUPPLY MEA NS Irl .lllh mW-h?! y mvElvroR Karl Mario Groetschel ATTORNEYS United States Patent O 3,145,964 HYDRAULC MINE PROP Karl Maria Groetsehel, Stolzestrasse 44, Bochum, Westphalia, Germany Filed May 9, 1963, Ser. No. 279,168 Claims priority, application Germany May 12, 1962 12 Claims. (Cl. 248-354) y The present invention relates generally to mine props, and, more particularly, to a device for increasing the setting force of hydraulic mine props with respect to the setting force imparted to the props `by means of a pressure medium acting upon the piston area of the prop.

Hydraulic props comprising inner and outer prop sections which are used for the continuously substituted or travelling support of the face of the mine or the mine working area are usually set in place with a setting force which is determined by the supply pressure of the hydraulic medium. Such props have high pressure relief valves which are set to the pressure of the roof of the mine which is normally of the magnitude of about 750 atmospheres. However, under the assumption that there is a pressure in the supply system for the hydraulic pressure medium of, for example, 100 atmospheres, when setting the props, with a normal force or load of the prop being 30 tons, such a small setting force is provided that only a fraction of the bearing capabilities of the prop are utilized in this phase of the operation.

However, in many cases, and particularly under the conditions which are encountered at present in modern mechanical mining operations such as coal mining systems having travelling hydraulic supports, it is desired to have a substantially greater setting force available for the props with the object of controlling the roof as completely'as possible. This is especially true for supporting arrangements which operate with supporting assemblies, and particularly such assemblies comprising a threeor four-leg trestle as a rear assembly and a hydraulic prop as the forward assembly.

During the development of the above-mentioned supporting arrangements, the desire has arisen for a simple and effective device making it possible to provide a substantial increase in the setting force and especially of the forward props of such assemblies. This is desired in order to provide the possibility of increasing the setting force at the freshly uncovered coal face or the working area of the mine, substantially beyond that of known hydraulic props of normal diameter and if possible to a multiple of the setting force of known props.

With these defects of the prior art in mind, it is a main object of the present invention to provide a device for a mine prop which satisfies the above-mentioned desire in the art.

Another object of this invention is to provide a device of the type described which is so constructed that the increase in the setting -force may occur at any desired instant and thus not necessarily immediately after setting the prop with its normal setting force, but at any subsequent time which may be chosen depending upon the condition of the roof.

A further object of the invention is to provide a device of the character described wherein the increase in the setting force can be made effective in a diiferentiated manner.

Still another object of the invention is to provide an arrangement wherein the setting load of mine props may be increased, and the increase may be determined previously and may be controlled when applied.

Still a further object of the invention is to provide a hydraulic prop having the above-mentioned features for increasing the setting force, but which is nevertheless capable of being exchanged and moved from location to ice location and set up within a location as simply and quickly as a prop which does not incorporate such a device.

Yet another object of the present invention is to provide a hydraulic prop having a device for increasing the setting force thereof and which does not substantially limit the extensibility or length of telescoping of the prop.

Yet a further object of the invention is to provide a prop having a device for increasing the setting force thereof which does not cause an increase in the stroke length of the prop when it is temporarily removed, since such an increase would impair the ability of the prop to be immediately reused in the face area of the mine at that particular time.

These objects and others ancillary thereto are accomplished according to preferred embodiments of the invention wherein a hydraulic pressure assembly is used which encloses one end of the prop with which it is to be used and which is itself independent and of a short stroke in comparison with the stroke of the prop. This pressure assembly has a piston which directly carries the prop and the piston area of the pressure assembly is substanftially larger, and at least twice as large as the piston area of the prop. The piston at its unstressed side has the configuration of a housing or receptacle and it encloses the prop end which is inserted into the hollow space thereof. This pressure assembly is preferably arranged coaxially with the prop.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when takenin conjunction with the accompanying drawing wherein the sole ligure is a side view, partially in section illustrating an embodiment of the present invention.

' Normally the prop and the additional pressure assembly have force applied thereto by the same source of pressure medium. However, it is also possible to connect the cylinder chamber of the additional pressure assembly to a separate system which delivers a pressure medium under substantially higher pressure.

Usually, the pressure assembly would be provided at ythe bottom end of the prop. However, it is also possible to mount it at the head or top of the normal prop and in this type of construction, the inner bottom surface of the piston, which is lfashioned as in the first embodiment as a receptacle, is preferably provided with a downwardly extending projection. This projection together with a corresponding recess in the prop head of the otherwise normally constructed prop, and which is easily and quickly interchangeable at any time, forms a joint which permits a limited and relatively universal pivotal movement of the parts with respect to each other. In both arrangements the prop can be easily exchanged.

With more particular reference to the drawing, a prop is illustrated which includes an inner prop section 1, which forms the piston, and an outer prop section 2 forming the cylinder of a normal hydraulic prop with telescoping sections. The lower end or foot 3 of the outer prop section 2 is inserted into a receptacle-like or pot-shaped chamber 4 of a piston 4 of the pressure increase assembly and this piston 4 thus encloses the foot 3. Although the piston 4 encloses foot 3 of the outer prop section 2, the foot is spaced from the inner surfaces of piston 4 by a predetermined spacing which is lled with resilient intermediate layers 5 which prevent the prop from pivoting laterally.

The pressure increase assembly includes a cylinder 6 in which the piston 4 is guidably moved and this piston is provided with an upper stop or abutting ring 12 for limiting the stroke of piston 4. A layer 11, similar tolayer 5, is disposed on ring 12 and at the top of cylinder 6. A connection conduit 8 is provided as the inlet and outlet for the pressure medium and inthe illustrated pre-Y ferred embodiment, the opening is connected via conduit 8b with the supply pipe 8a for the pressure medium which normally serves via conduit 8c for providing pressure medium to the prop and so no extra line is needed for the extra assembly. Under certain circumstances, the opening can also be connected with a special feed pipe for a medium which is at a higher pressure than that of the normal hydraulic system for the prop.

As is shown in the drawing, the effective surface of the piston 4 is substantially larger than the effective area of the piston formed by the lowersurface of inner prop 1. Considered from the point of the desired and obtainable effect, it does not make any difference whether the pressure increase assembly is provided at the head or at the foot of the prop whose setting force is to be increased. In the drawing the arrangement at the foot of the prop is illustrated and structure is also shown for forming a pressure increase assembly at the head. The assembly which is provided at the head is basically the same as that described above, and it is placed at the top of the inner prop section. This assembly comprises a pressure cylinder 17 having an inlet and outlet opening 16 and a piston 19 which is arranged in the form of a receptacle.

In accordance with the illustrated preferred embodiment of the invention the inner bottom surface of this piston is provided with a downwardly extending projection 22 which engages a recess at the top surface of the prop head and thus, together with the recess forms a joint. A stop ledge or flange 18 is provided in cylinder 17 in order to limit the stroke of the piston. In this arrangement also the intermediate space between the periphery of the inner prop section and the inner surface of piston 19 may be, and preferably is, filled with resilient filler elements 5'.

If special roof conditions make it advisable, it is also possible to utilize the lower and upper assemblies together, with these two assemblies preferably being provided with different size piston areas in order to suitably supplement the setting possibilities. In this case it is of no importance and only determined by considerations as to suitability whether or not the assembly is provided with the smaller piston area at 'the head or at the foot of the piston prop.

In the embodiment which is shown, the pressure increase assembly in which the outer prop section is disposed is provided with a further feature of the invention by arranging the cylinder body 6 of the first assembly as the piston of a second assembly and inserting this cylinder body in a further pressure cylinder 25. This cylinder 25 has an inlet and outlet opening 28. Cylinder 25 also is provided with a stop 27a for limiting the stroke of the piston 6. This stop cooperates with a counter stop 27 provided in the form of a ring on a cylindrical extension sleeve 26 or the like attached to the cylinder 25. By means of this arrangement further possibilities are provided for increasing the setting force pressure. In operation, the simplest case for the setting of a normal single prop will be considered. The operation is as follows: First the prop which is provided with the pressure assembly is fully extended and the setting operation is performed as is done with a normal hydraulic prop and with its own relatively low setting force by applying pressure between the prop sections 1 and 2, acting as a cylinder and piston. This may be done by admitting the pressure medium from supply line 8a to line 8c via cock 30.

At a desired instant, the prop is provided with the desired setting load or force by placing the pot-shaped piston of the pressure assembly under pressure preferably by means of a normal pressure medium supply through the use of the three-Way cock 30 and line 8b, and the pressure of the prop against the roof is increased in correspondence with the relationship of the effective area of the piston of the additional assembly with respect to the area of the end of the prop piston proper. When the additional pressure assembly is used, the cock 30 admits pressure medium to line 28' to thus operate the piston 6.

In a similar manner and by a slight change in connections the upper pressure increase assembly may be operated. If the upper and lower assemblies are to be used together, suitable connections can be added for supplying pressure to the upper cylinder.

The piston and cylinder arrangements shown have cylinders open to the atmosphere so that only a single pressure medium connection for each cylinder is needed. The weight of the apparatus will be sufficient to retract the pistons once there is release of the pressure medium acting upon the pistons.

As a numerical example, the new device makes it possible to increase the force, using a pressure of the hydraulic pressure medium of atmospheres and, for example, the setting force of 4 tons of a prop, which can normally be achieved. Such a prop has a normal load of 30 tons, and the setting force can then be increased to 20 tons, if the size of the piston area of the additional pressure assembly is five times the size of the piston area of the prop. For example, if the prop piston has an area of 40 cm.2, the additional pressure assembly piston would have an area of 200 cm?.

A setting force of this magnitude could otherwise only be achieved by a corresponding increase of the prop diameter, and thus of the effective piston area of the prop itself, and vthis increase is not possible due to economic reasons and mine operation problems.

The use of this new additional setting force increasing device provides special advantages at least for setting the forward prop and/or for the forward trestle of a support assembly constructed of such a trestle as well as a rearward trestle which can travel with the assembly and be moved with respect to the forward trestle. For example, if the rear trestle of such an assembly is provided with four props each having 40 cm.2 piston area, a 'total setting force of the rear trestle of 16 tons results using a pressure in the supply pipe for the hydraulic system of 100 atmospheres.

If a one-prop forward trestle is used together with such a rear trestle and this has an effective piston area which amounts to, for example, 50 cm?, then this trestle with the same pressure of the hydraulic medium will have a setting force of 5 tons. This setting force can be increased to the same amount as that of the rear trestle of 16 tons or even higher, for example, 20 tons, by using a pressure increasing assembly having a piston area of cm.2 or 200 cm?.

The pressure cylinders of the novel pressure increasing assemblies usually do not require a pressure relief valve of their own, because the hydraulic prop and/or support of the trestle or frame, chosen in number and their supporting capabilities correctly for the support of a working area, is not in danger of being completely pushed in or buckling when yielding to the pressure of the rock or the subsidence of the mine. They are not rigid and as a means for protecting these pressure increase cylinders against overload, the same pressure relief valve provided for the prop proper against overload may be used. The devices and systems for controlling the feed and discharge pipes of the pressure medium are the conventional types and valves of the multiple-way cock type or the like may be used, although they are not specifically illustrated in the drawing.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.v

What is claimed is:

1. In a hydraulic mine prop using a pressure medium acting upon a piston to provide a prop setting force, the improvement comprising: means for increasing the setting force of a prop and including a hydraulic pressure assembly having a short stroke in comparison to the pressure medium supply means connected to introduce Y pressure medium to the prop.

4. The arrangement as defined in claim 3 wherein said assembly includes a pressure cylinder deiining a chamber connected to said pressure medium supply means for the prop.

5. The arrangement as deiined in claim 3 wherein said assembly includes a pressure cylinder deiining a chamber and a separate pressure medium supply means is provided which is at a substantially higher pressure than said prop pressure medium supply means, said separate supply means being connected to said cylinder chamber.

6. The combination as deined in claim 1 wherein said pressure assembly is connected to the foot of the prop, and a further pressure assembly is provided which is connected to the head of t-he prop.

7. The combination as deined in claim 6 wherein the piston areas of said pressure assemblies lare different.

8. The combination as defined in claim 1 wherein said piston formed as a receptacle encloses and supports the end of the prop, and resilient means are provided between said prop and the inner surface of said piston.

9. The combination as dened in claim 1 wherein said pressure assembly is provided at the head of such prop, the inner bottom surface of the piston formed as a receptacle having a projection extending downwardly 'and forming a joint with a corresponding recess in the prop head.

10. The combination as defined in claim 1, comprising a further and correspondingly fashioned pressure assembly slightly larger than said lirst-recited pressure assembly, said rst-recited pressure :assembly including a cylinder having a lower cylinder surface arranged within said second pressure assembly and forming the pressure piston of said further pressure assembly.

11. A hydraulic mine prop, comprising, in combination:

(a) an eXtensible telescopic prop including an inner section acting as a piston Within an outer section acting as a cylinder;

(b) pressure medium supply means connected to supply pressure medium to the cylinder; and

(c) a device for increasing the setting force of said prop and including a hydraulic pressure assembly having a short stroke in comparison to the stroke `of said prop, said assembly being operable independently of said prop and having a piston formed as Ia receptacle and surrounding and holding the end of one of said prop sections, said assembly having a piston area which is substantially larger than the piston area of said prop.

l2. A hydraulic mine prop, comprising, in combination:

(a) an extensible telescopic prop including an inner section acting as a piston within an outer section acting as a cylinder;

(b) pressure medium supply means connected to supply pressure medium to the cylinder;

(c) two hydraulic pressure assemblies for increasing the setting force of said prop, each having a short .stroke in comparison to the stroke of said prop and being operable independently of said prop, each assembly including (l) a cylinder defining a chamber,

(2) a piston formed as a receptacle and surrounding and holding the end of one of said prop sections so that one piston holds the head of the prop and the other piston holds the foot of the pro-p, the piston area of said piston being at least twice as large as the piston area of said prop, the inner bottom surface of the piston holding the head of the prop having a downwardly eX- .tending projection forming a joint with a corresponding recess in the prop head, and

(3) resilient means disposed between said prop and the inner surface of said piston to prevent lateral movement of the prop with respect to such piston; and

(d) a further and correspondingly fashioned pressure assembly slightly larger than said rst-recited pressure iassemblies, one `of said first-recited pressure assemblies having a cylinder land a lower cylinder surface which is arranged Within said second pressure assembly to form the pressure piston of said further pressure assembly.

References Cited in the file of this patent UNITED STATES PATENTS 762,627 Fink June 14, 1904 2,473,687 Kershaw June 21, 1949 2,754,804 Miller July 17, 1956 FOREIGN PATENTS 877,869 Great Britain Sept. 20, 1961 918,561 Germany Sept. 30, 1954 960,463 Germany Mar. 21, 1957 1,125,863 Germany Mar. 22, 1962 

1. IN A HYDRAULIC MINE PROP USING A PRESSURE MEDIUM ACTING UPON A PISTON TO PROVIDE A PROP SETTING FORCE, THE IMPROVEMENT COMPRISING: MEANS FOR INCREASING THE SETTING FORCE OF A PROP AND INCLUDING A HYDRAULIC PRESSURE ASSEMBLY HAVING A SHORT STROKE IN COMPARISON TO THE STROKE OF A PROP, SAID ASSEMBLY ENCLOSING AN END OF SUCH PROP BUT BEING OPERABLE INDEPENDENTLY THEREOF, SAID ASSEMBLY HAVING A PISTON FORMED AS A RECEPTACLE FOR EMBRACING THE END OF SUCH PROP, SAID PISTON HAVING A PISTON AREA WHICH IS SUBSTANTIALLY LARGER THAN THE PISTON AREA OF SUCH PROP. 